Heavy oil catalytic cracking is an important process for producing lower olefins such as ethylene, propylene and butylene.
The commercial process of heavy oil catalytic cracking to produce lower olefin includes those disclosed in U.S. Pat. No. 4,980,053, U.S. Pat. No. 5,670,037 and U.S. Pat. No. 6,210,562. These processes use a single riser reactor or a combination of a single riser reactor and a dense bed and have problems of high dry gas and coke yields.
Recently, more and more attentions are paid to the technology of using two risers to produce propylene.
CN101074392A discloses a method for producing propylene and gasoline diesel-oil by two-section catalyzed cracking style, which is carried out by adopting two-section lift pipe catalyzing process and catalyst with molecular sieve, taking heavy petroleum hydrocarbon or various animal and vegetable oils containing hydrocarbon as raw materials, optimization combining by charging style for various reactants, and controlling proper reactive conditions. It can improve propylene and light-oil recovery rate and quality, and inhibit to generate dry gas and coke. Said method has a low propylene yield and a low heavy oil conversion capability.
CN101293806A discloses a catalytic conversion method for improving the yield of low-carbon olefin, which comprises the following steps: hydrocarbon oil raw material is injected into a riser or/and a fluidized bed reactor via a feed nozzle, comes into contact with catalyst containing shape-selective zeolite with an average pore size being smaller than 0.7 nm and reacts; gas rich in hydrogen is injected into the reactor; reaction oil gas and spent catalyst after reaction are separated, wherein the reaction oil gas is separated to obtain a target product containing ethylene and propylene; and the spent catalyst is returned to the reaction for reutilization after being stripped and regenerated. By injecting gas rich in hydrogen, the method can remarkably inhibit reconversion reaction of the generated low-carbon olefin to improve the yield of low-carbon olefin, particularly of propylene. Said method has a limited effect of decreasing the dry gas yield and increasing the heavy oil conversion capability.
CN101314724A discloses a method for catalytically transforming bio-oil and mineral oil combination, which comprises the following steps: contacting bio-oil and mineral oil with catalyst containing modified beta-zeolite in a compound reactor to carry out catalytic cracking reaction, separating the reaction resultant with the spent catalyst, processing the spent catalyst by stripping and burning and adding into the reactor for recycling, introducing the separated resultant from the reactor, and distilling to obtain target product low-carbon alkenes, gasoline, diesel and heavy oil. Said method has a high dry gas yield and a low heavy oil conversion.